In this proposal we describe experiments which have as their goal the definition of the functions of the eosinophil in human disease. As a means to this end we propose to isolate eosinophils from human blood and determine the subcellular origin of the Charcot-Leyden crystal (CLC). We also propose to prepare antisera to the CLC and the major basic protein from the human eosinophil and to use these antisera (1) for measurement of the CLC protein and the major basic protein in body fluids, cells and tissues and (2) for localization of these proteins in inflamed tissues characterized by eosinophil infiltration. The crystalline core of the eosinophil granule will be purified and its contents analyzed. Finally, the osmiophilic bodies associated with eosinophils will be isolated and analyzed.